Organophosphorus pesticides are agricultural chemicals that are most widely used and are marketed for the purpose of controlling pests. These organophosphorus pesticides are less persistent than organochlorine pesticides, and thus have a lower residual risk. In addition, these have strong pesticidal activity, but are highly toxic for humans and livestock, and need to be used in relatively large amounts because these have low persistence. Organophosphorus pesticides that are frequently used include diazinon, iprobenfos, edifenphos, dichlorovos, parathion, malathion, and EPN (o-ethyl-o-(p-nitrophenyl)-phenyl phosphothioate.
Residual pesticides that are low-molecular-weight toxic chemicals are concentrated in the body even in small amounts and show toxicity, and thus adversely affect human health and the ecosystem. For this reason, continuous analysis and environmental monitoring for detecting the presence of pesticides are required, and a system for performing such analysis and monitoring needs to be introduced.
However, the conventional analysis of residual pesticides is performed using instrumental analysis methods that require expensive systems and professional manpower and mostly require large amounts of time and money. For this reason, it is required to develop a biosensor system capable of detecting residual pesticides in situ in a convenient and rapid manner.
Conventional systems for detecting organophosphorus pesticide residue using AChE (acetylcholinesterase) or OPH (organophosphate hydrolase) have disadvantages in that expensive enzymes and complex experimental procedures are required, a plurality of sample solutions should be separately prepared, and reactions between enzymes and substrates are time-consuming.
For example, a nano-biosensor for detecting pesticides using liposomes (Vicky Vamvakaki et al., Biosens. Bioelectron., 22(12): 2848-2853, 2007) is based on the principle in which AChE hydrolyzes nano-sized liposome complexes to generate a fluorescence signal, and the intensity of the fluorescence is reduced due to the decrease in the degree of the hydrolysis when the activity of the enzyme is reduced by the pesticide, and this change in the fluorescence is measured. However, it has disadvantages in that a process for forming liposome complexes is complicated, and many kinds of reagents, including buffer, liquid nitrogen and 5,5′-dithiobis-nitro-benzoic acid (DTNB), are required.
In addition, an optical biosensor for detecting organophosphorus compounds using OPH (organophosphate hydrolase) and gold nanoparticles (A L Simonian et al., Anal. Chim. Acta., 534(1):69-77, 2005) is also based on a fluorescence detection method. In this method, OPH-gold nanoparticle conjugates are formed using ester, and when 7-hydroxy-9H-(1,3-dichloro-9,9-dimethylacridin-2-one) (DDAO) phosphate is added to the conjugates, the DDAO phosphate bind to the conjugates and shows fluorescence by the gold nanoparticles. In this case, when an organophosphorus pesticide is present, OPH binds to the pesticide while it becomes distant from the DDAO phosphate and gold nanoparticles, and thus the intensity of the fluorescence decreases. This change in the fluorescence is measured. However, this method has disadvantages in that the reagents and time for conjugating OPH to gold nanoparticles are required and the limit of detection is low.
Meanwhile, gold nanoparticles are nanomaterials that are most widely used in the biosensing field, and have various specific properties that do not appear in general organic materials. Thus, many sensor systems have been developed using gold nanoparticles. Gold nanoparticles have an extinction coefficient that is about 103-105 higher than that of general organic dyes, and thus have a characteristic UV/Vis spectrum. Also, the intensity and sensitivity of the spectrum are high, and thus a change in color from red to blue according to the distance between gold nanoparticles occurs rapidly, and an invisible change in the color can be detected by measuring the spectrum.
The discussions in the foregoing background section is to provide general background information, and does not constitute an admission of the prior art.